1. Field of Invention
This invention relates to a head up display system, and in particular to an automotive windshield with the combiner for a head up display system incorporated into the automotive windshield.
2. Technical Considerations
A head up display system is a system that displays information to a viewer while he simultaneously views the real world around and through the display. A head up display system is often incorporated into aircraft cockpits for pilots to monitor flight information, and more recently the systems have been used in land vehicles, such as cars, trucks and the like The display system is generally positioned so that the viewer does not have to glance downward towards the vehicle dashboard and away from the viewing area in front of the vehicle as is normal for vehicle operation to view the operating information.
Head up display systems generally include a display projection system, a collimator and a combiner. The projection system includes a light source that projects operating information through the collimator which generally aligns the projected light rays. The collimated light is reflected off the combiner, which is a wavelength selected element positioned in a portion of the operator field of view, such that the operating information which is reflected off the combiner may be easily viewed by the operator. Depending on how the collimator aligns the projected light rays, the reflected image may be focused anywhere from a position immediately in front of the vehicle to optical infinity.
The combiner may be any wavelength selective reflective material such as a holograph or reflective metallic film. In a holographic head up display windshield system, the combiner is a hologram which may be applied to a film carrier and positioned in the interlayer between the transparent glass plies of the windshield. It can be appreciated that a head up display system providing important vehicle information such as, for example, fuel supply and vehicle speed positioned within the motorist field of vision through the windshield will permit the motorist to safely maintain eye contact with the real world while simultaneously viewing the display information.
The interlayer material in a windshield is typically a heat sensitive material, such as polyvinylbutyral, which flows during the windshield laminating operation. When the holographic combiner is embedded within the interlayer, the combiner may distort due to the flowing characteristics of the interlayer material, adversely affecting its reflective properties and optical quality of the windshield. In addition, the combiner reduces the windshield optical quality by introducing additional materials between the windshield glass plies.
It would be advantageous to have the combiner as thin as possible and to maintain the combiner surface parallel to the major surfaces of the glass plies so as to reduce optical distortion through the windshield and maintain the reflective properties of the combiner.